17 December 2014

Long-lived lightning clusters in hotspots worldwide

Posted by kwheeling

By Leslie Willoughby

Most lightning hits as a short-lived luminosity, a flickering flash in the pan. Other lightning lingers 10 to 100 times as long. It can simmer the sap of an entire tree and spark a dangerous forest fire. Now, researchers at the University of Alabama in Huntsville have identified hotspots worldwide where long-lived lightning clusters occur.

This video shows short-lived lightning, the kind that occurs 90 percent of the time.
Credit: UAH Phillip Bitzer, T. Daniel Walker

Long-lived lightning, called continuing current lightning, is thought to be responsible for destructive events associated with lightning, such as forest fires. Lightning ignited 9,000 wildland fires per year on average between 2008 and 2012, according to an online report by the National Fire Protection Association. A new satellite sensor might help scientists give early warning to firefighters about these forest fires, according to Phillip Bitzer, a lightning physicist at the University of Alabama in Huntsville.

“Most people talk about lightning flashes as if they’re all the same thing. But when you open the lightning box, you start seeing all the different lightning attributes that can be very important,” Bitzer said Monday at the American Geophysical Union’s Fall Meeting in San Francisco.

Phillip Bitzer maintains a lightning monitor in his backyard in Huntsville Alabama. His dog avoids it, but only because one time it ran into a monitor support while chasing a ball. Credit: Christy Bitzer

Phillip Bitzer maintains a lightning monitor in his backyard in Huntsville Alabama. His dog avoids it, but only because one time it ran into a monitor support while chasing a ball.
Credit: Christy Bitzer

For his research, Bitzer studied continuing current lightning that persists 10 milliseconds or more. The human eye can barely detect a difference between this type of lightning, which amounts to only 10 percent of land-based flashes, and the more common faster lightning. Either type could be missed in the blink of an eye, which can take 100 milliseconds. The difference plays out in raging forest fires, fried electrical equipment and other damage caused by continuing current lightning.

Scientists observed that there seems to be less lightning of any kind over the ocean than over land. Bitzer wanted to learn where in the world continuing current lightning occurs most frequently.

To find out, he studied signatures of 17 million lightning flashes that have been gathered by a Lightning Imaging Sensor located on a satellite in near-earth orbit.

The LIS is limited in its ability to identify strikes that come to ground, said Don MacGorman, a physicist at the National Severe Storms Laboratory in Norman, Oklahoma, who was not involved in the study. To account for that limitation, Bitzer used ground-based networks to fine-tune the information.

Bitzer found when flashes happen over the ocean they are more likely to be continuing current lightning than is the case when they occur over land.  In an unexpected finding, he discovered that continuing current lightning clusters along the east coast of the United States. He also found hotspots along the southeast coast of Africa and along the east coast of Australia.

The presence of continuing current lightning can indicate the approach of a severe storm, and the earliest warning possible can provide those in the storm’s path life-saving time to seek shelter. But radar — the fastest weather warning available — takes five minutes to refresh. Bitzer envisions having the capability someday to detect continuing current lightning in real time. That capability might provide five more minutes’ warning before a storm. And it might point firefighters to a location to monitor for new wildland fires before they explode into unmanageable conflagrations.

This video shows damaging and less common long-lived, or continuing current, lightning.
Credit: UAH Phillip Bitzer, T. Daniel Walker

Bitzer’s next step will be to study lightning detected by a new satellite. The National Oceanic and Atmospheric Administration, in cooperation with NASA, plans to launch the first-ever geostationary lightning mapper by early 2017. Unlike the previous LIS satellite, this one will travel in a higher and geostationary orbit. That difference will allow scientists to observe a single storm as it takes place and may make Bitzer’s vision a reality.

“The biggest difference is we will be able to watch a single storm evolve in real time, delivering data to decision makers in just tens of seconds,” Bitzer said. That’s not lightning fast, but it could be a life-saving improvement, he added.

-Leslie Willoughby is a science communication graduate student at UC Santa Cruz.